Abstract: A composition consisting essentially of a perovskite crystalline structure includes ions of a first metal M1 which occupies an A-site of the perovskite crystalline structure and ions of a second metal M2 which occupies a B-site of the perovskite crystalline structure. M2 has two oxidation states capable of forming a redox couple suitable for reversibly catalyzing an oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER). The composition also includes ions of a third metal M3 at least a portion of which substitutes for M1 in the A-site of the perovskite crystalline structure, and at least a portion of which optionally also substitutes for M2 in the B-site of the perovskite crystalline structure. At least some of the ions of M3 have a different oxidation state to the ions of M1. The composition also includes atoms of an element X, which is a chalcogen.

Abstract: Provided is a composition comprising: (a) a principal phase that is provided by a layered mixed metal oxide having a rocksalt structure belonging to the R-3m space group; the layered mixed metal oxide comprising the following component elements: 45 to 55 atomic % lithium; 20 to 55 atomic % of one or more transition metals selected from the group consisting of chromium, manganese, iron, nickel, cobalt, and combinations thereof; and 0 to 25 atomic % of one or more additional dopant elements selected from the group consisting of: magnesium, calcium, strontium, titanium, zirconium, vanadium, copper, ruthenium, zinc, molybdenum, boron, aluminium, gallium, tin, lead, bismuth, lanthanum, cerium, gadolinium and europium; wherein said atomic % is expressed as a % of total atoms of said layered oxide, excluding oxygen; (b) a minor phase that is provided by a metal oxide that does not have the crystal structure of the layered mixed metal oxide, the minor phase comprising one or more of the transition metals contained in

Abstract: A composition consisting essentially of a perovskite crystalline structure, the composition comprising: ions of a first metal M1 which occupies an A-site of the perovskite crystalline structure; ions of a second metal M2 which occupies a B-site of the perovskite crystalline structure, M2 having two oxidation states capable of forming a redox couple suitable for reversibly catalyzing an oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER); ions of a third metal M3 at least a portion of which substitutes for M1 in the A-site of the perovskite crystalline structure, and at least a portion of which optionally also substitutes for M2 in the B-site of the perovskite crystalline structure, at least some of the atoms M3 having a different oxidation state to the atoms M1; and atoms of an element X, which is a chalcogen; wherein the metal ions M1, M2 and M3 are present in the atomic ratios (a) or (b): (a) 25 to 49.